Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
In an electric motor, cogging torque is defined as the torque that results from the interaction between the permanent magnets of the rotor and the geometry of the stator slots. Under light loads and at low speeds, cogging torque may prevent smooth rotation of the rotor, and cause speed ripple, vibration, or jerkiness. Cogging torque is dependent on the position of the electric motor. Further, under ideal conditions, the cogging torque as a function of position may be periodic. The number of magnetic poles and the number of teeth on the stator can affect the periodicity per revolution of the ideal cogging torque.
Electric motors may exhibit non-ideal cogging torque when in rotation. For example, imperfections in the construction of the electric motor or non-idealistic properties of magnetics used in the electric motor may cause irregularities in the cogging torque. This non-ideal cogging torque may cause the electric motor to prefer to settle in one position over another, if the first position is a lower energy state.
Additionally, if an electric motor is installed in a robot actuator, irregularities in the cogging torque of the electric motor can influence the ability of the robot actuator to accurately track a trajectory. This effect may be particularly pronounced in low-cost, outrunner motors, such as those used in electrically propelled, radio-controlled (RC) model aircraft, due to the orientation of the magnets. Most RC outrunner motors have a unique construction as a result of the low-cost, non-repeatable assembly processes that are often used to manufacture the motors.